Field of the Invention
The present invention deals with a lighting unit energized from a 110 volt 60 hertz source in which the principal source of light is an arc lamp supplemented by a standby filamentary lamp, and which includes a power supply unit providing high frequency energy for starting the arc lamp while using dc for normal lamp operation.
The present invention deals with a lighting unit in which the principal source of light is a high pressure discharge lamp having up to six times the efficient of an incandescent lamp. High pressure metal vapor lamps have been available for some time in high power units. Recently, as disclosed in U.S. Pat. No. 4,161,672, smaller, low wattage metal halide lamps with efficiencies approaching those of the larger size have been invented. Such lamps are an energy efficient replacement for the incandescent lamp. When part of a lighting unit suitable for home use, provisions must be made for standby illumination and assuming two light sources, means must be provided for supplying the diverse electrical requirements of the two light sources.
The power supply of the present lighting unit employs a high frequency power supply in which a ferrite transformer controlled for non-saturated operation, a transistor switch, and a trigger oscillator are the principal components. Such power supplies have been termed static inverters in deference to the fact that "dc" quantities are converted to ac through static or non-moving parts. The inverter and ferrite transformer herein described are the subject of U.S. Applications Ser. No. 47,972 and Ser. No. 969,281.
In the starting sequence, such a power supply will initially produce high frequency energy at a high voltage for starting the arc lamp, after which the power supply reverts to a dc mode in which continuous dc is supplied. In such supplies, failure of the arc lamp may cause the supply to remain in the starting mode for an indefinite period. Continued operation in the starting mode is undesirable, resulting in the production of unnecessary electromagnetic interference and wasted power.